1. Field of the Invention
The present invention relates to slew-rate control, and in particular relates to an apparatus and method for controlling the slew-rate of an interface.
2. Description of the Related Art
Low-power transmitters, frequently used in mobile phones, cameras and displays, are interfaces for signal communications. FIG. 1A is a schema showing a typical connection between two interfaces 100 and 110. The master interface 100 is electrically coupled to the slave interface 110 (which is regarded as a capacitance load), and transmits signals to the slave interface 110 via the pad 120. For operation speed and EMI reasons, the signals transmitted on the interfaces 100 and 110 are slew-rate controlled.
To address the explosive growth in the mobile industry, the Mobile Industry Processor Interface (MIPI) Alliance was created to define and promote open standards for interfaces. D-PHY is the physical layer specified for several of the key protocols within the MIPI family of specifications. The MIPI specification for D-PHY has defined various allowable slew-rate ranges for various capacitance loads. For example, the slew-rate shall be 30-100 mV/ns for a capacitance load of 70 pF, while the slew-rate shall be 30-500 mV/ns for a capacitance load of 0 pF. FIG. 1B illustrates an example signal, which conforms to the allowable slew-rate range limited by the MIPI D-PHY specification.
The slew-rate of a low-power transmitter can be optimized for a particular load or designed to have a moderate value for various loads during manufacturing stages. However, when actually utilized, the slew-rate of a low-power transmitter can not be optimized for all kind of loads. Therefore, it is desirable to provide a new apparatus and method for controlling the slew-rate of an interface.